The present invention relates to a thin film two terminal element used in a switching element, etc., of an active matrix type liquid crystal display device, a flat panel display, etc.
A typical thin film two terminal element is an MIM element. This MIM element is typically constructed by using Ta as a lower electrode, Ta.sub.2 O.sub.5 (anode oxide film) as an insulating film and Cr or Cr/ITO as an upper electrode. In particular, when this MIM element is used in a switching element of the liquid crystal display device, the Cr/ITO also has a function of a picture element electrode and two layers are continuously formed. Further, a heat processing is performed at a temperature about 300.degree. to 500.degree. C. to obtain a symmetric property of polarity, as proposed by Japanese patent application Laying Open (KOKAI) No. 62-62333. An insulating film using SiN.sub.x by a plasma CVD method is proposed as the above insulating film in Japanese patent application Laying Open (KOKAI) No. 61-260219 and NIKKEI ELECTRONICS published on Jan. 12, 1987. In this layer structure, ITO is used as the lower electrode(picture element electrode), SiN.sub.x as the insulating film, and Cr is used as the upper electrode.
However, in the MIM element using the anode oxide film as the insulating film, the following three disadvantages are caused.
(1) The insulating film is limited to the anode oxide film of a lower metal so that it is impossible to control its matter property value and therefore arbitrarily control MIM element characteristics.
(2) It is necessary to perform the heat processing at the temperature about 300.degree. to 500.degree. C. so that a substrate material used in this MIM element is limited to have a high heat resistance.
(3) The dielectric constant of this element is high. Accordingly, when this element is used as the switching element of the liquid crystal display device, it is necessary to reduce the element area in consideration of the restriction in which the MIM capacity divided by the liquid crystal capacity is less than 1/10. Therefore, a high fine processing is required.
Further, in the MIM element using SiN.sub.x as the insulating film, the disadvantages of the above items (1) and (3) are solved, but the disadvantages of the item (2) are left since the film forming temperature is about 300.degree. C. and is therefore high. Further, pin-holes tend to be caused by dust, etc., and the yield is reduced.
Further, when the above element is used as the switching element of the liquid crystal display device, there is a processing in which a photolitho-etching is performed with respect to this element after a material for the lower electrode of the two terminal element is stacked on a transparent electrode (picture element electrode). In this case, a defect in the transparent electrode is caused in a developing process in a certain case.